using System;

public class Program

{

    private static void Main(string[] args)

    {

        string input1 = "hello world";

        string expected1 = "helo wrld";

​

        string input2 = "this is a test";

        string expected2 = "this a est";

​

        string input3 = "a1a2a3a4a5a6";

        string expected3 = "a12a34a56";

​

        string output1 = Process(input1);

        string output2 = Process(input2);

        string output3 = Process(input3);

​

        Console.WriteLine($"Input:  [{input1}] Output:  [{output1}] Expected: [{expected1}] Matches: [{string.Equals(output1, expected1)}]");

        Console.WriteLine($"Input:  [{input2}] Output:  [{output2}] Expected: [{expected2}] Matches: [{string.Equals(output2, expected2)}]");

        Console.WriteLine($"Input:  [{input3}] Output:  [{output3}] Expected: [{expected3}] Matches: [{string.Equals(output3, expected3)}]");

    }

​

    private static string Process(string input)

    {

        //No build in functions allowed, no lamda, no linq.

        string output = string.Empty;

        char[] inputCharArray = input.ToCharArray();

​

        foreach (char c in inputCharArray)

        {

            output += c;

        }

​

        return output;

    }

}